1. Technical Field
This invention relates generally to ion generators and ion wind devices, and more specifically to an improved method and apparatus for reducing the ozone output from ion wind devices.
2. Background Art
Ion wind devices such as described in Lee U.S. Pat. No. 4,789,801 provide accelerated gas ions through the use of differential high voltage electric fields between one or more emitters and an array of collectors (accelerators). The ions are entrained in the ambient bulk gases, causing the gases to flow. Gas velocities can reach as high as eight hundred feet per minute. However, the high voltage electric fields used to generate the gas ions and provide the force necessary for gas acceleration are also responsible for creating molecular dissociation reactions, the most common of which include ozone generated from oxygen when such devices are operating in a breathable atmosphere. It is an object of this invention to provide methods to reduce the ozone output by converting the produced ozone back to oxygen.
The U.S. Food and Drug Administration has determined that indoor airborne ozone in concentrations above 50 ppb (parts per billion) may be hazardous to humans. NIOSH has ruled that indoor concentrations of ozone above 100 ppb may be hazardous to humans. Devices which utilize high voltage electric fields to generate atmospheric plasma, corona discharge and air ions are all susceptible to generating the allotrope, ozone. There exist a linear relationship between the level of the high voltage fields and current and the level of ozone concentration in most direct current operated ion wind systems. Also, a linear relationship exists between the acceleration velocity and intensity of the electric fields (typically the higher the voltage the higher the acceleration). Since it is desired to have maximum acceleration, methods must be employed to limit or eliminate unwanted ozone output.
When ozone is produced in ion wind devices it may be converted back to oxygen by using various materials placed in or downstream from the airflow. Noble metals such as gold, silver or platinum may be plated to the leading edge (or the entire surface) of the accelerator array substrate to function as a catalytic converter to convert the ozone to oxygen. However, precious metal plating may not be a practical method of catalyzing ozone due to the high cost of the precious metal material itself. Accordingly, the invention discloses a method to plate manganese dioxide onto accelerator substrate elements which also reduces, through catalytic conversion, ozone levels. The MnO2 coating will catalyze ozone to from O2 (O3-O2) thus reducing ozone from the airflow. Activated carbon coatings may also be used for the purpose of converting ozone to oxygen.
The disclosed manganese plating and oxidation process has proven successful in reducing by greater than 20% the concentration of ozone downstream from the primary emissivity source.